The antigen-antibody reaction is the basis for all immunological test methods. Special proteins called antibodies are produced by an animal in response to the presence of an antigen, that is a foreign protein, in the body fluids of the animal. This normal body response to a foreign protein has led to the development of a number of techniques which are used to diagnose various human and animal diseases or disorders. Immunological test methods have also been used to detect pregnancy. In vitro tests for the presence of a suspected antigen or antibody in a body fluid are carried out by adding the immunological counterpart to a vial of the body fluid, i.e., add antigen if the test is for the presence of antibody or add antibody if the test is for the presence of antigen. If the suspected protein is present the resulting antigen-antibody reaction is generally manifested by precipitation or agglutination of the antigen-antibody complex. As used herein the term body fluid refers to urine, serum, plasma, or the like. In some instances the antigen-antibody complex is slow to form and the particles that are formed are too small to be observed with certainty. In such cases, detectability of the antigen-antibody reaction can be improved by utilizing a carrier. When the antigen or antibody is coated on the surface of a carrier the reaction with the immunological counterpart produces a visible mass or agglutant. The proteinic antigen or antibody may be adsorbed onto the surface of carriers such as erythrocytes, bacterial cells, bentonite, polystyrene latex particles, anionic phenolic resins, or finely divided diazotized amino cellulose. It has been found, however, that chemical binding of the antigen or antibody molecule to the carrier is superior to physical adsorption. U.S. Pat. No. 3,857,931 teaches that proteinic antigens or antibodies can be attached chemically by the formation of an amide bond to a polymer latex carrier having surface carboxyl groups.
The art also teaches that amine-bearing bodies such as peptides and proteins can be chemically attached to polyacrylamide beads by partial hydrazinolysis of surface acrylamide groups followed by a diazotization reaction and the subsequent reaction of the azide formed with a peptide or protein. See U.S. Pat. No. 3,853,987; Inman et al. Biochemistry 8, 4074 (1969); Vieth et al. Chemtech, p. 47, January (1974); Barber et al., Process Biochem, p. 14, August 1970. However, the techniques described are unsatisfactory for use with a latex system which requires special procedures to prevent destabilization of the colloidal system.